material that is neither a conductor nor an insulator but can be chemically altered to be
either one.
You may have noticed that many of the places where high-tech manufacturing com-
panies are located have taken on nicknames like Silicon Valley (California), Silicon Alley
(New York), and Silicon Glen (Scotland).Conductors and Insulators
A material that is aconductorallows electrical current to pass through it. Without getting
too technical, materials like copper, aluminum, or gold are good conductors of electricity
because they have free electrons through which the current can pass.
On the other hand, a material that does not allow an electrical current to pass through
it is called aninsulator. Insulators like rubber, wood, or glass do not have many free
electrons through which the current can pass.
Those materials that, depending on their chemical make-up, will or will not allow
electricity to pass are calledsemiconductors,which means they can be altered chemically
to be either a conductor or an insulator. Silicon is a semiconductor. However, when it is
combined with phosphorus, it picks up some extra electrons and becomes a conductor;
when it is combined with boron, which lacks electrons, it becomes an insulator. By
mixing silicon with phosphorus or boron, it can be either a conductor or an insulator,
whichmakessilicontheperfectmaterialfortransistorsandotherelectroniccomponents.How an IC Is Made
Thecreationofamicrochipisaveryinvolvedchemicalprocess.Ifyouwantanexcellentex-
planation and look at how an integrated circuit is manufactured, visit the “How Micro-
chips are Made” Web site provided by the Intel Corporation atwww.intel.com/home/
howto/basics/chips/. However, here is a brief summary of what happens in this process:- A seed crystal is slowly dipped into a molten silicon bath. As it is slowly
extracted, it grows into an ingot of pure silicon that is ground into a perfect
cylinder. A very thin wafer is sliced from the cylinder and polished. - The wafer is exposed to some gases at very high heat. This allows a very
thin layer of silicon dioxide, like rust on metal, to form on the wafer. - The wafer is coated with a chemical calledphotoresist, which is resistant to
ultraviolet (UV) light, and then dried. The photoresist softens when exposed
to UV light. - A stencil mask is placed over the wafer, and it is exposed to UV light. The parts
of the wafer that are not shielded by the mask become soft and gooey. Solvent
is used to remove the soft photoresist material, leaving behind the pattern
created by the mask. - The exposed silicon diode is removed with other chemicals, which exposes
the base silicon wafer in those places left open by the mask. The remaining
(^46) PC Hardware: A Beginner’s Guide